Photography basics: Understanding aperture

17 November 2016

Aperture is one of the three pillars of photography, the others being shutter speed and ISO. These three make up the basics to be able to use your camera out of auto mode and be a lot more flexible with your photography so understanding them is key to taking your photos to the next level.

I will try and explain aperture as simply as possible because this is the most complicated of the three pillars, but it tends to be the most talked about because it can really alter the feel of a photo.

So, what actually is aperture?

As simply as possible - aperture is a hole in your camera lens that lets in light, it can be changed to be big or small to let in more or less light to the sensor.

The easiest way to think of this concept is to think of your own eyes, the pupils specifically. The pupil changes size to let in less or more light depending on how bright the object is that you are looking at. To see this in action; Look into a mirror in a dark room for 30 seconds, then turn on a torch pointing at your face - watch how your pupils go from large to small when you turn on the torch. This is because in the dark room your eyes need as much light as possible to help you see, so the pupil is large, then you turn the light on and the pupil is letting in way too much light so it shrinks in size to combat this.

So, when your pupils are small, this is known as a small aperture and when they are large this is a large aperture.

How do we control aperture?

Aperture is controlled and expressed in f-numbers (for example f/2.2 or f/8). These f-numbers are known as f-stops and are used as a way of describing how open or closed an aperture is.

A smaller f-stop means a larger aperture, whereas a larger f-stop means a smaller aperture. Confusing, I know. People are used to larger numbers representing larger things, but aperture is the opposite.

Take a look at this chart below that visually displays aperture. The size of circle represents aperture along with their corresponding f-numbers (image courtesy of Wikipedia):

What is depth of field?

Depth of field is a side effect of changing the aperture, it creates an area of the image that appears sharp while the rest is blurry.

A large f-number of f/22 (a small aperture) will produce pretty much no blur, meaning the foreground and background will both be in focus and sharp. A small f-number of f/1.8 (large aperture) will make only the foreground sharp, the background will be out of focus. See our example below:

35mm | f/1.8 | 1/40 sec | ISO 200

35mm | f/22 | 1/5 sec | ISO 800

Lenses have aperture limits

Every lens has a maximum and minimum aperture, you should be able to see what these limits are in your lenses spec and sometimes printed on the lens itself.

The maximum aperture (small f-number) is a lot more important than the minimum, this is because most lenses offer a minimum of at least f/16 which is more than enough where maximum apertures of f/1.4 or above can be harder to come by.

A high max aperture lens is known as a fast lens because it can let in a lot more light and so is suited to low light situations, so if you want to photograph in low light or you are looking to get as much depth of field as possible then find a lens with a high max aperture.

Aperture can be a pretty hard pillar to learn - the best way to do so would be having a play around with the settings on your camera to try out some different f-stops and see what effect it has on your images!